The present invention relates to a so-called resolver for measuring or determining of angle positions or revolutions of a shaft by using an inductive magnetic field between a stator and a rotor connected or connectable to said shaft.
Such devices consist in principle of sensors which measure angles or revolutions by using the inductance principle. With existing devices the needed inductance coils are installed in the stator and rotor. In resolvers which have to establish particularly the exact angle position of the rotor the required coils have to be mounted by hand, which is very expensive to do.
This very expensive production technique limits the versatility of the usual type of resolvers.
It has been tried to reduce the production costs by mounting the inductance coils only on the stator and to give the rotor an elliptical shape, thus allowing the determination of the exact angle position of a shaft. Eliptical rotors are, however, very expensive to manufacture as well.
It is an object of the present invention to build up a resolver much simpler, in order to reduce the production costs and to allow versatility of the models to be produced. At the same time, it be of course required that the accuracy is at least as good, if not better than that of presently used resolvers.
Resolvers are particularly used for industrial automation and motion controls.
In order to solve this problem the resolver in accordance with the invention is characterized in that the stator only is provided with an induction coil and a measuring coil, whereas the rotor is equipped on its circumference with a number of pole surfaces of differing polarity which interact with said stator coils, whereby the pole surfaces are formed in such a way as to present in each angle position of the rotor a reluctance which is specific for this position.
Preferably the pole surfaces of the rotor are formed as slight protrusions on the rotor circumference. The pole surfaces, seen over the whole circumference, may continuously change their surface or be of a shape that the airgap between the pole surface and the corresponding stator part will continuously differ in each angle position (continuous change).
These pole surfaces 6,7 as illustrated in FIG. 1, are shaped such that they generate in each position of the rotor 5 an inductance specific for each position. This variable inductance can be obtained by a continuously changing of the pole surfaces (surface) or by different thickness of said protuberances, leading to different heights of the airgap of the active pole surface between rotor and stator.
This very simple design of the proposed resolver allows every exact measurement and accurate determination of the angle position of the rotor over 360xc2x0.
Any other shape and arrangement of the magnetic pole surfaces of differing polarity are of course within the scope of the invention.
In a special embodiment of the invention the effective pole surface of each polarity extend over 180xc2x0 of the rotor circumference and vary continuously from a minimum to a maximum.
The rotor can be placed in an axial passage of the stator 29, as shown in FIG. 3, or the sleeve shaped end section of the rotor comprising the effective pole surfaces can extend into the axial gap of the stator. Whereby the induction coil and the measuring coil of the stator may be positioned on one or the other side of the rotor extension.
In principle the rotor can also be positioned. in a radial gap of the stator whereby the stator coils should be positioned, similar as in the execution with the axial gap, on both sides of the pole surfaces of the rotor.